Helicity of N, N′-diaryl- trans-1,2-diaminocyclohexane derivatives. Implications for molecular helicity manipulations

Abstract

Derivatives of trans-1,2-diaminocyclohexane (DACH), useful as chiral ligands, scaffolds and building blocks, differ in their conformation. The conformation of N, N′-diaryl-DACH derivatives was studied by the semiempirical and DFT computational methods and by exciton-coupled circular dichroism. It was found that, contrary to M-helical N, N′-diimine, N, N′-diimide and N, N′-diamide derivatives, the aromatic residues in N, N′-diphenyl derivatives are oriented to form a P- helix for the ( R, R)-DACH absolute configuration. The helicity of the bis-aryl system is modified in the case of 1-naphthyl or 2-naphthyl derivatives. Further switching of helicity has been demonstrated by either protonation or mono- N-acetylation of N, N′-diaryl DACH derivatives.